We have reported that a novel c-Myc binding protein, AMY-1, stimulated the transcription activity of c-Myc and was translocated from cytoplasm to nuclei in a c-Myc-dependent manner. Here, the role of AMY-1 in cell differentiation was examined. AMY-1 expression was up-regulated after differentiation induction of human K562 cells to erythrocyte cells by AraC, while c-Myc expression was rapidly down-regulated. K562 cell lines expressing exogenous AMY-1 were established, and these cells expressed a high level of epsilon-globin mRNA, a marker gene necessary for erythrocyte cell differentiation, without differentiation induction. The addition of AraC rapidly initiated differentiation in these cell lines, which continued to differentiate to erythrocyte cells possessing a high level of hemoglobin even after the decrease in AMY-1 expression. These results suggest that AMY-1 is a trigger for K562 cells to differentiate to erythrocyte cells and that AMY-1 may have a function independent of or different from c-Myc.